Evaluating Your Dog’s Hips
Hip dysplasia can be a heartbreaking condition, especially when it causes pain and difficulty moving in a young dog. In order to identify affected dogs – dogs with abnormal hip structure – there are two common diagnostic systems: PennHIP and OFA. Both rely on x-ray images of a dog’s hips to identify degenerative changes in hip joints. In addition to looking at the structure of the joint, PennHIP also measures hip laxity, and provides a predictor of future hip health for the dog.
Breeders who want to avoid producing puppies that will have early onset of severe hip dysplasia should evaluate the hips of the dogs they plan to breed. While the severity and progression of hip dysplasia is affected by both genetic and environmental factors (such as diet and exercise), breeders can tip the odds in favor of producing good hips by evaluating the prospective parents and their close relatives to determine level of risk.
PennHIP uses three different x-ray views of the hips to inform their reports. The main item reported is the dog’s Distraction Index (DI) for each hip. The DI is a measure of how lax or tight the hip joints are. Any arthritic changes in each hip are also identified. The DI for each hip can range from 0.0 to 1.0, with 0 being extremely tight hips and 1 being extremely loose hips. DIs below 0.3 indicate that the dog is at low risk for developing hip dysplasia, while numbers above 0.7 indicate the dog is at high risk for arthritic changes in the hip over time. Numbers between 0.3 and 0.7 indicate an increasing, but likely manageable, risk of arthritis. This is where managing the dog’s weight, making sure it gets appropriate exercise, and feeding high quality food, make the difference between an unaffected dog and an affected dog.
OFA reports are based on a single x-ray view and the report tells you whether the dog currently has any arthritic changes or joint abnormalities. Results range from OFA Excellent, through Good, Fair, and Borderline, and then to Mildly, Moderately, or Severely Dysplastic. Both OFA and PennHIP reports provide useful information for breeders. PennHIP provides more information and an actual measurement of laxity; it can be done on dogs under a year of age. Dogs are not eligible for certification by OFA until they are 2 years of age.
How To Read A Hip X-Ray
The x-ray view used by OFA is called a “hip extended” view. The dog is positioned on his/her back and their hind legs are extended straight down so that their femur (thigh bones) are roughly parallel and their kneecaps centered over their knees in the picture. The radiologist evaluates the structure of the hip joint to determine how well-formed the joint is and to assess if there are any degenerative changes or signs of arthritis. In order to get the best view of the joint it is important that the dog be positioned properly.
The x-ray here is of a dog with normal hips. Things to note:
- Positioning: the areas outlined in blue can be used as landmarks to determine if the dog is well-positioned for the x-ray. The blue areas should be symmetrical. If a dog is rotated so the x-ray view is not straight-on, the right and left sides will look different because of the rotation. That can present a misleading view of the hip conformation.
- Head and Neck of Femur: the head of the femur (red) should be round and smooth, seated deep in the hip socket; the neck of the femur should be well defined with a notch on the top line. A deformed or flattened head of the femur, or thickening of the femoral neck, are signs of degenerative changes.
- Pelvic Acetabulum: the hip socket (green) should be deep, forming a smooth cup for the head of the femur. You can see the shadow of the rim of the acetabulum as a faint line showing through the ball of the femur. Using that line as a landmark, hips that merit OFA rating of “Good” or better generally have at least 50% of the ball of the femur seated in the socket.